This invention relates to a combinatorial weighing apparatus and, more particularly, to a combinatorial weighting apparatus of the type that operates by finding the weights of articles charged into a plurality of weighing hoppers, and discharging from proper ones of the weighing hoppers those articles which, in combination (referred to as the "best" combination"), give a total weight equal to a set target weight or closest to the set target weight within preset allowable limits.
It is general practice to employ a computerized combinatorial weighing apparatus, referred to as a computer scale, when weighing out a category of articles having widely different unit weights from one to another. Examples of such articles are vegitables and fruits, confectioneries, perishables and fabricated parts. As shown in FIG. 1, a combinatorial weighing apparatus of the aforementioned type operates by measuring the weights of articles charged into a plurality of weighing hoppers 2-1, 2-2, . . . 2-n, the measurements being performed by weighing machines 3-1, 3-2, . . . 3-n provided on the respective weighing hoppers, selecting the combination of articles that gives a total weight closest to a preset target weight within preset allowable limits, the selection being based upon the weights measured by the weighing machines, discharging the selected articles from the weighing hoppers containing them, collecting the discharged articles in a collecting chute 4 and delivering them to a timing hopper 5, subsequently replenishing the emptied weighing hoppers with new articles to be weighed, finding the next combination of articles to be discharged, and then repeating the foregoing cycle to continue the weighing out of articles in automatic fashion.
FIG. 2 illustrates the general construction of the combinatorial weighing apparatus described above. Numeral 1 denotes a dispersing table of vibratory conveyance type. Articles to be weighed are introduced onto the dispersing table 1 and imparted with vibratory motion for a predetermined length of time so as to be dispersed radially outwardly from the center of the table. Numerals 2-1, . . . 2-n denote n-number of weighing stations which are arranged around the dispersing table 1 along radially extending lines to receive the articles dispersed by the table. Each weighing station includes a dispersing feeder 2a, a pool hopper 2b, a pool hopper gate 2c, a weighing hopper 2d, a weight sensor (weighing machine) 3, a weighing hopper gate 2f, and a hopper drive unit 2g. The dispersing feeder 2a is an independently vibratable conveyance device for feeding the articles by means of vibration, and includes an electromagnet 2a-1 and a trough 2a-2 which is vibrated by the magnet 2a-1. Each dispersing feeder 2a is so arranged that the articles received from the centrally located dispersing table 1 can be introduced into the corresponding pool hopper 2b disposed therebelow. The pool hopper gate 2c is provided on each pool hopper 2b in such a manner that the articles received in the pool hopper 2b are released into the weighing hopper 2d when the pool hopper gate 2c is opened under the control of the corresponding hopper drive unit 2g. Each weight sensor 3, accompanying a respective one of the weighing hoppers 2d, is operable to measure the weight of the articles introduced into the corresponding weighing hopper, and to apply an electrical signal indicative of the measured weight to a combination control unit, shown in FIG. 2. The combination control unit then selects the combination of articles (known as the "best" combination) that gives a total weight equal to a target value or closest to the target value within preset allowable limits, as will be described below in further detail. Each weighing hopper 2d is provided with its own weighing hopper gate 2f. Only the weighing hopper gates 2f of those weighing hoppers that give the best combination are opened under the control of the hopper drive units 2g, these gates 2f discharging the articles into a common chute 4 where they are collected together. The collecting chute 4 has the shape of a funnel and is so arranged as to receive the articles from any of the circularly arrayed weighing hoppers 2d via the hopper gates 2f, which are located above the funnel substantially along its outer rim. The articles received by the collecting chute 4 are collected at the centrally located lower end thereof by falling under their own weight or by being forcibly shifted along the inclined wall of the funnel by a mechanical scraper or the like, which is not shown.
In operation, articles are charged into each of the pool hoppers 2b and weighing hoppers 2d. The weighing sensors 3 associated with the weighing hoppers 2d measure the weights of the articles and supply the combination control unit, not shown, with signals indicative of the measured weight values, denoted L.sub.1 through L.sub.n. The combination control unit computes combinations based on the weight values L.sub.1 through L.sub.n and selects the best combination of articles that gives a total weight closest to a target weight within preset allowable limits. The hopper drive units 2g respond by opening the prescribed weighing hopper gates 2f based on the best combination, whereby the articles giving said best combination are released into the collecting chute 4 from the corresponding weighing hoppers 2d to be fed into the timing hopper 5. This will leave the selected weighing hoppers 2d empty. Subsequently, therefore, the pool hopper gates 2c corresponding to the empty weighing hoppers 2d are opened to introduce a fresh supply of the articles from the respective pool hoppers 2b into said weighing hoppers 2d, leaving these pool hoppers 2b empty. Accordingly, the dispersing feeders 2a which correspond to the empty pool hoppers 2b are vibrated for a predetermined period of time to deliver a fresh supply of the articles to these pool hoppers. This restores the weighing apparatus to the initial state to permit resumption of the control operation for selecting the best weight combinations in the manner described. Thus, weighing by the combinatorial weighing apparatus may proceed in continuous fashion by repeating the foregoing steps.
FIGS. 3 and 4 illustrate another example of a combinatorial weighing apparatus of the above type, improved to raise the discharge rate of the articles. Here the apparatus is provided with inner and outer chutes 4a, 4b having upper open ends 4c, 4d which are concentrically arranged, and lower open ends 4e, 4f arranged side by side, with the inner chute 4a penetrating through the conical wall of the outer chute 4b at the middle portion thereof. Each of the weighing hoppers 2-1, 2-2, . . . 2-n is provided with a pair of independently openable weighing hopper gates 2f.sub.1, 2f.sub.2. According to this arrangement, opening predetermined ones of the weighing hopper gates makes it possible to discharge articles selectively into the inner and outer chutes 4a, 4b from the weighing hoppers. With a combinatorial weighing apparatus of this kind, the weights of the articles fed into the weighing hoppers 2-1, 2-2, . . . 2-n are weighed by the respective weight sensors 3-1, 3-2, . . . 3-n, and signals indicative of the weighed values are sent to a combination control unit, which is not shown, for computing combinations based upon these weight values. More specifically, the combination control unit is adapted to either (a) simultaneously select two "best" combinations giving first best and second best values equal to a target weight or closest to the target weight within preset allowable limits, or (b) select one "best" combination, as defined above, and then recompute combinations based on the remaining weight values and select another single "best" combination based on this second round of computations. When two sets of combinations have been selected through either of the above methods, the weighing hopper gates 2f.sub.1, 2f.sub.1 . . . of the weighing hoppers corresponding to the first selected combination are opened to discharge their articles into, say, the inner chute 4a, and the weighing hopper gates 2f.sub.2 , 2f.sub.2 . . . of the weighing hoppers corresponding to the second selected combination are opened to discharged their articles into the outer chute 4b. Both sets of the discharged articles are collected by the respective inner and outer chutes 4a, 4b and delivered to timing hoppers 5, 5'.
Various configurations of the above-described combinatorial weighing apparatuses exist, but in all of them one or a plurality of combinations are selected in each single weighing cycle, and the articles are discharged from the selected weighing hoppers at one time. In other words, with the conventional combinatorial weighing arrangements, a discharge command signal is transmitted to all of the selected weighing hoppers simultaneously, causing these hoppers to release their articles into the chute 4 (FIG. 1), or into the inner and outer chutes 4a, 4b (FIG. 3), at the same time. As the articles discharged en masse in this fashion converge at the bottom opening of the chute, therefore, the opening is likely to be blocked as articles of a poor flowability exhibit a bridging phenomenon and pile up faster than they can be delivered from the opening. This makes it impossible to deliver the articles to the awaiting timing hopper. An additional defect is exhibited by the combinatorial weighing apparatus of FIG. 3 having two article discharge paths, wherein the discharged articles, irrespective of their flowability, form bridges and pile up also at the portion of the outer chute 4b, where it is narrowed by the intersecting inner chute 4a, when a large quantity of the articles are released into the outer chute 4b at one time. This prevents the delivery of the articles from the outer chute.